Well, we already know wizards can die.

Regardless of not showing Radagast in the three LotR films, in the books Radagast plays a very important role. I know PJ has deviated in many places across the four films so far (I haven't seen DoS so I can't speak directly to that but I'm sure it's safe to guess "5 films so far"), but his deviations have not been dramatic to the point of breaking core Tolkien that much.

IMO, so far you could watch the Hobbit movies and STILL read the LotR books without major issues in addition to blending with the films. If Radagast is killed off then his presence in the LotR books becomes a major conflict. PJ may be taking some creative and dramatic freedoms but I'm not aware of any place he has created a major issue like that. It could be argued that the Scouring scene does this but Saruman and Wormtongue are each do die before the end of the RotK so killing them earlier in TTT is not a critical factor, and film-wise cutting the Scouring was necessary for time limitations (though I really wished they were able to film it for Extended).

I can see the "yard sale" return of Bilbo as being in the 3rd film. The birthday party scene at the start of FotR and H:UJ each point to his on going issues with the Sackville Baggins and he specifically mentions her trying to make off with his spoons. In RotK we had many loose ends to tie up including Aragorn (king + Arwen), the young Hobbits return and departure to the West. In Hobbit we have Bilbo return to the selling of his home and goods and then a follow up visit by one of the Dwarves. Not nearly as much to worry about as far as screen time goes. I would like to see the visit because I think it is strong to the character development that has taken place between both as well as giving some good chance for humor (how the Hobbits of the Shire look at an armored Dwarf martching up to Bag End in the middle of the day).

I'm curious to see if Dol Guldur is dealt with fully or only partially. In the time of the Hobbit it should only be a partial event as Dol Guldur remains a deadly threat into the War of the Rings when it is finally destroyed. But since PJ doesn't touch on the existence or role of the fortress at all in his LotR films he's free to have the utter destruction of Dol Guldur in the third film. In fact, if he DOESN'T do it in the third film there will probably be people not familiar with the books asking why doesn't it have any role in the LotR. Again, this is in alignment with my Radagast-can't-die argument above. Dol Guldur IS destroyed in the LotR by the Elves but not in any way that is seen of disussed on film, so if it is destroyed by the Elves in the Hobbit it doesn't really trip up too much of the LotR books. Radagast has some importance in the LotR books and never dies so killing him in the 3rd Hobbit film would be 'wrong'.

Of course, PJ has consulted with me about as much as GW has so this is all just my own expertly determined but never requested opinion.

If Tauriel will be killed, please let it happen early on in the third movie. Saves another two hours of all that.. ..
DoS spent twice as much time on that awful storyline as on Beorn. Can't end soon enough.

As for Dol Guldur, they can simply make it similar to the book version: White Council repels the Necromancer, think they've done a good job, while Sauron flees to Mordor and starts his project there - which nicely bridges to LotR. No need to destroy the fortress if it is deemed empty and harmless (as both the audience and the White Council can think).

I really didn't mind the Kili/Tauriel stuff, I think all this talk of a 'romance' is grossly exaggerating what was shown in the film as opposed to an infatuation on KIli's part and an interest in other cultures on Tauriels.